Extracorporeal lithotripters for the noninvasive disintegration of kidney stones are well known. Such lithotripters use a truncated ellipsoidal reflector with an open end that is closed by a rubber or the like diaphragm. The interior of the reflector and the space defined by the diaphragm are filled with water. A spark gap is provided at the first focus point of the reflector. The second focus point of the reflector is positioned outside of the reflector and beyond the diaphragm. The reflector and the patient are moved relative to one another to position the second focus point on the kidney stone or other bodily concretion to be disintegrated. A spark across the spark gap flashes some of the water into steam and generally produces a shockwave. The shockwave is focused by the reflector and passes through the water in the reflector, through the diaphragm, and through bodily tissues to the kidney stone on which it is focused. A succession of such shockwaves reduces the kidney stone to small fragments that readily pass out of the body with the urine.
In many sophisticated lithotripters the positioning is done by means of X-rays or ultrasound. As is known, the amount of exposure permitted to X-rays is limited. Ultrasound devices are usually interconnected with a computer so that when the kidney stone is properly located by the ultrasound transducer the computer relatively moves the patient and the reflector to cause the second focus point to coincide with the kidney stone. Such use of a computer and centering mechanisms materially increases the cost of the lithotripter, and thereby makes it unavailable to many prospective patients.
Use of an ultrasound transducer mounted within the lithotripter reflector and on the rotational axis thereof is disclosed in U.S. Pat. No. 4,620,545 issued to Shene, Nowacki and Brisson. A conical shield is interposed between the spark gap and the ultrasound transducer. However, no details are disclosed as to the mounting of the shield or the transducer relative to the reflector, or relative to one another.